1. Field of the Invention
The present invention relates to a variable power finder, and more particularly to a variable power finder suitable for a digital camera or the like, which is small in size and has an excellent optical performance, and also to an imaging apparatus using the same.
2. Related Art
Conventionally, in a camera in which a photographing system and a finder system are separately configured, where the photographing system has a variable power function, the variable power function corresponding to the variation in an imaging angle of view is also configured in the finder system. As the above-mentioned finder system, real image type variable power finders, in which the visibility of a view frame is good and a predetermined variable power ratio is easily obtained, are variously proposed.
As the real image type variable power finder, those disclosed in Patent Document 1 and Patent Document 2 below are known. They are provided with a negative first lens group, a positive second lens group and a positive third lens group, as an objective optical system. They try to shorten the entire length by dividing an inverting optical system which converts an inverted image taken by the objective optical system into an erecting image and by displacing a part of reflection unit to a back focus unit of the objective optical system.
Also, in Patent Document 3, it is designed to further shorten the entire length by placing a third lens group on the incident surface of the inverting optical system.
[Patent Document 1] Japanese Patent Application Publication No. JP-A-Heisei 1-116616
[Patent Document 2] Japanese Patent Application Publication No. JP-A-Heisei, 4-194913
However, the trend toward compact models of the digital cameras in recent years has been progressed more than expected, and the further reduction in the entire length of the objective optical system is required. So, in order to attain the further miniaturization from the present situation, it is necessary to make the refractive force of each lens group stronger. However, it is very difficult to excellently compensate the various aberrations induced in the respective lens groups while maintaining the predetermined variable power ratio.